1. Field of the Invention
This invention is directed to the production of useful agglomerates or aggregates of finely divided particulate matter.
2. Description of the Prior Art
There is currently produced in the United States untold quantities of finely divided materials which because of their very highly subdivided or dust-like form have little if any utility. The particles are, for all intents and purposes waste or at best semi-waste materials. A good example of such finely divided materials is fly ash which is a by-product of coal-fired boiler power plants, currently being produced in the United States at an estimated rate of 20 to 25 million tons per annum. Considerable money and effort have been expended toward the development of products and/or uses of fly ash both in its generated state or by agglomerating it by various methods. One of the major hurdles which proponents of fly ash utilization have failed to negotiate successfully has been handling and transportation. The material sizes out from minus 60 mesh to a theoretical plus 10,000 and definitely poses serious problems unless properly confined. Special equipment is required and apparently those materials which fly ash is attempting to supplant do not demand what amounts to additional cost. Accordingly, any proposed utilization of this waste material would have to include consideration of the fact that it cannot competitively be handled, stored or transported in its generated state. It must be agglomerated, preferably at a point of origin.
Another hurdle is the rather uneviable position of those industries generating fly ash, notably utilities, who are by far the largest producers. For some 40 years various utilization schemes have been researched either internally or through independent organizations and, although a small measure of divergent product has been obtained, it is quite apparent there is an enormous gap between generation and utilization, and what is even more appalling, it is widening. Dumping of fly ash is costly and proposed anti-pollution activity on the part of political sub-divisions, no matter how laudable, will present additional cost as time passes. The dilema of those generating fly ash is this: They cannot afford to process any less than total ash produced at any one point otherwise dual handling costs add more expense to existing costs. Utilities are unable to market fly ash in any great quantity as raw materials for various uses because of sales expense involved as well as the generally held concept of avoiding competition with customers in these fields. So, any proposal aimed at solution of this problem will have to remove the total ash at any point of generation before a utility could justifiably consider deviation from present practice.
The above discussions of the problems presented by fly ash and the needs which clearly exist for methods of successfully agglomerating the same into useful products applies equally to a host of other products amongst which can be included finely divided particles of refractory and siliceous materials, crystalline materials, combustible carbonaceous materials and the like.
While a variety of agglomerating methods and binders have been heretofore utilized for agglomeration of these fine particles, the methods and products they produce have not been without their shortcomings. It is known, for instance, to utilize sodium chloride as a binder in the agglomeration of such finely divided materials. However, the products obtained by such methods have been disappointedly fragile even where the agglomerated particles have been sintered above the melting point of the particles to effect fusion thereof.
One of the objects of the invention, therefore, is to provide a method for agglomerating finely divided particulate material into strong aggregates of high density.
Another object of the invention is to provide lightweight aggregate which has been heated or roasted to provide a product which possesses an unusually high porosity while maintaining at the same time excellent strength.
Yet another object of the invention is to provide a method of agglomerating waste and semi-waste particulate materials in a convenient fashion so as to alleviate the pollution problems currently caused by the dumping of such materials. An independent analysis of effluent resulting from the dumping of fly ash shows the following:
______________________________________ PARTS PER MILLION Fe-Al Acid Salts 50. CaCO.sub.3 448. Sulphate 753. Chloride 48. Acid Index (ph) 3.5 ______________________________________
The raw Fly ash analysis is as follows:
______________________________________ Moisture .37% SiO.sub.2 34.90 Iron-Alumina Oxides 60.39 CaO 2.05 MgO 1.55 Sulphur .74 ______________________________________
When one considers the fact that just a single power generating facility introduces waste material, namely fly ash, at a rate of 2,000 tons daily, and this product is composed of the above contaminants, into the environment, subject to the elements at all times, the enormity of the situation emerges. For instance, sulphur, when combined with water produces sulphuric acid. Potentially, a simple calculation results in the realization that some 15 tons of sulphur, leached by water which is inevitable as the particles are minute, eventually will find its home in the water table, and this happens each day. Over a period of a year the final result amounts to a possible 1,358,000 gallons of sulphuric acid siphoning into the already dwindling fresh water supply of the world. Certainly, a sobering prospect, especially upon consideration that this is just one utility station.
These and other objects of the invention will become apparent from the following description of the invention and the appended claims.